Lubricating compositions comprising a volatility reducing additive

ABSTRACT

A lubricating composition is provided comprising: (i) a base oil; and (ii) a volatility reducing additive; wherein the composition has a kinematic viscosity at 100° C. (according to ASTM D445) of 16.3 mm2/s or less, a low temperature cranking viscosity of at most 6200 cP at −35° C. (ASTM D5293) and a NOACK volatility of at most 15% according to ASTM D5800B.

BACKGROUND

The present invention relates to lubricating compositions comprising abase oil and a volatility reducing additive for particular use in thecrankcase of an internal combustion engine, in particular an internalcombustion engine used in a passenger vehicle or light duty van.

In practice, various lubricating compositions for crankcase engines areknown. A disadvantage of low viscosity crankcase engine oils is thatthey they may have undesirably high volatility, in particular asmeasured by the ASTM D5800B NOACK volatility test.

Attempts have been made to overcome the above problems by formulatingwith low volatility base oils, such as Fischer-Tropsch derived baseoils. WO2010020653 discloses the use of Fischer-Tropsch base oils inlubricating compositions. The composition of Example 1 of WO2010020653shows a surprisingly low NOACK volatility when compared to thecomposition of Comparative Example 1 (using a Group III mineral baseoil).

However, for future low viscosity engine oils such as 0W-16 (as per SAEJ300 table of engine oil viscosity grades) and lower viscosities (0W-12,0W-8, etc), additional benefits beyond those conferred via the use ofFischer-Tropsch base oils may be desired.

It has surprisingly been found that by including certain lubricantadditives in the lubricating formulation the NOACK volatility can belowered.

SUMMARY

According to the present invention, there is provided a lubricatingcomposition comprising:

(i) a base oil; and

(ii) a volatility reducing additive;

wherein the lubricating composition has a kinematic viscosity at 100° C.(according to ASTM D445) of 16.3 mm²/s or less, a low temperaturecranking viscosity of at most 6200 cP at −35° C. (ASTM D5293) and aNOACK volatility of at most 15.0% according to ASTM D5800B.

According to another aspect of the present invention, there is providedthe use of a volatility reducing additive for reducing the NOACKvolatility of a lubricating composition, in particular wherein thelubricating composition comprises a Fischer-Tropsch base oil.

DETAILED DESCRIPTION

The base oil used in the present invention may conveniently comprisemixtures of one or more mineral oils and/or one or more synthetic oils;thus, according to the present invention, the term “base oil” may referto a mixture containing more than one base oil. Mineral oils includeliquid petroleum oils and solvent-treated or acid-treated minerallubricating oil of the paraffinic, naphthenic, or mixedparaffinic/naphthenic type which may be further refined byhydrofinishing processes and/or dewaxing.

Suitable base oils for use in the lubricating oil composition of thepresent invention are Group III mineral base oils, Group IV poly-alphaolefins (PAOs), Group III Fischer-Tropsch derived base oils and mixturesthereof.

By “Group III” and “Group IV” base oils in the present invention aremeant lubricating oil base oils according to the definitions of AmericanPetroleum Institute (API) for category III and IV. These API categoriesare defined in API Publication 1509, 15th Edition, Appendix E, April2002.

Fischer-Tropsch derived base oils are known in the art. By the term“Fischer-Tropsch derived” is meant that a base oil is, or is derivedfrom, a synthesis product of a Fischer-Tropsch process. AFischer-Tropsch derived base oil may also be referred to as a GTL(Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oilsthat may be conveniently used as the base oil in the lubricatingcomposition of the present invention are those as for example disclosedin EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029029, WO 01/18156 and WO 01/57166.

Synthetic oils include hydrocarbon oils such as olefin oligomers(including polyalphaolefin base oils; PAOs), dibasic acid esters, polyolesters, polyalkylene glycols (PAGs), alkyl naphthalenes and dewaxed waxyisomerates. Synthetic hydrocarbon base oils sold by the Shell Groupunder the designation “Shell XHVI” (trade mark) may be convenientlyused.

Poly-alpha olefin base oils (PAOs) and their manufacture are well knownin the art. Suitable poly-alpha olefin base oils that may be used in thelubricating compositions of the present invention may be derived fromlinear C₂ to C₃₂, preferably C₆ to C₁₆, alpha olefins. Particularlypreferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene,1-dodecene and 1-tetradecene.

Preferably, the base oil as used in the lubricating compositionaccording to the present invention comprises a Fischer-Tropsch derivedbase oil.

There is a strong preference for using a Fischer-Tropsch derived baseoil over a PAO base oil, in view of the high cost of manufacture of thePAOs. Thus, preferably, the base oil contains more than 50 wt. %,preferably more than 60 wt. %, more preferably more than 70 wt. %, evenmore preferably more than 80 wt. %, most preferably more than 90 wt. %Fischer-Tropsch derived base oil.

The total amount of base oil incorporated in the lubricating compositionis preferably present in an amount in the range of from 60 to 99 wt. %,more preferably in an amount in the range of from 65 to 90 wt. %, andmost preferably in an amount in the range of from 70 to 85 wt. %, withrespect to the total weight of the lubricating composition.

According to the present invention, the base oil (or base oil blend)preferably has a kinematic viscosity at 100° C. of at least 3.0 cSt(according to ASTM D445), preferably between 3.0 and 4.0 cSt.

The lubricating composition of the present invention further comprises avolatility reducing additive. As used herein, the term “volatilityreducing additive” pertains to any compound added into a lubricatingcomposition at low levels (typically 1% or less) that confers areduction in NOACK volatility. Some examples of suitable volatilityreducing additives include, but are not necessarily limited to, anaminic anti-oxidant, molybdenum based friction modifier, and acombination thereof.

The volatility reducing additive may be present in the lubricatingcomposition on its own or as part of an additive package. The volatilityreducing additive is preferably present in the lubricating compositionin an amount in the range of from 0.5 wt. % to 5 wt. %, preferably 0.5wt. % to 2 wt. %, with respect to the total weight of the lubricatingcomposition.

As mentioned above, the lubricating composition according to the presentinvention meets certain specific requirements for the low temperaturecranking viscosity at −35° C., the kinematic viscosity at 100° C. andthe NOACK volatility. Typically, the low temperature cranking viscosityat −35° C. (according to ASTM D5293) of the lubricating composition isat most 6200 cP.

Typically, the kinematic viscosity at 100° C. (according to ASTM D445)of the lubricating composition is at most 16.3 cSt, preferably from 3.8to 16.3 cSt, and more preferably from 3.8 to 9.3 cSt.

Typically, the high temperature, high shear viscosity (“HTHS”)(according to ASTM D4683) of the lubricating composition is in the rangeof from 1.7 to 3.7 mPa·s, preferably in the range of from 1.7 to 2.6mPa·s.

Typically, the NOACK volatility (according to ASTM D5800B) of thelubricating composition is 15.0 wt % or below, preferably 12.5 wt % orbelow, even more preferably 10.0 wt. % or below.

The lubricating compositions according to the present invention mayoptionally further comprise one or more additives such as anti-oxidants,anti-wear additives, dispersants, detergents, overbased detergents,extreme pressure additives, friction modifiers, viscosity indeximprovers, pour point depressants, metal passivators, corrosioninhibitors, demulsifiers, anti-foam agents, seal compatibility agentsand additive diluent base oils, etc.

As the person skilled in the art is familiar with the above and otheradditives, these are not further discussed here in detail. Specificexamples of such additives are described in for example Kirk-OthmerEncyclopedia of Chemical Technology, third edition, volume 14, pages477-526.

Optional anti-oxidants that may be conveniently used in lubricantformulations include phenyl-naphthylamines (such as “IRGANOX L-06”available from Ciba Specialty Chemicals) and diphenylamines (such as“IRGANOX L-57” available from Ciba Specialty Chemicals) as e.g.disclosed in WO 2007/045629 and EP 1 058 720 B1, phenolic anti-oxidants,etc. The teaching of WO 2007/045629 and EP 1 058 720 B1 is herebyincorporated by reference.

Anti-wear additives that may be conveniently used includezinc-containing compounds such as zinc dithiophosphate compoundsselected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates,molybdenum-containing compounds, boron-containing compounds and ashlessanti-wear additives such as substituted or unsubstituted thiophosphoricacids, and salts thereof. Examples of such molybdenum-containingcompounds may conveniently include molybdenum dithiocarbamates,trinuclear molybdenum compounds, for example as described in WO98/26030, sulphides of molybdenum and molybdenum dithiophosphate.

Boron-containing compounds that may be conveniently used include borateesters, borated fatty amines, borated epoxides, alkali metal (or mixedalkali metal or alkaline earth metal) borates and borated overbasedmetal salts.

The dispersant used is preferably an ashless dispersant. Suitableexamples of ashless dispersants are polybutylene succinimide polyaminesand Mannich base type dispersants.

The detergent used is preferably an overbased detergent or detergentmixture containing e.g. salicylate, sulphonate and/or phenate-typedetergents.

Examples of viscosity index improvers which may conveniently be used inthe lubricating composition of the present invention include thestyrene-butadiene stellate copolymers, styrene-isoprene stellatecopolymers and the polymethacrylate copolymer and ethylene-propylenecopolymers. Dispersant-viscosity index improvers may be used in thelubricating composition of the present invention.

Preferably, the lubricating composition contains at least 0.1 wt. % of apour point depressant. As an example, alkylated naphthalene and phenolicpolymers, polymethacrylates, maleate/fumarate copolymer esters may beconveniently used as effective pour point depressants. Preferably notmore than 0.5 wt. % of the pour point depressant is used.

Furthermore, compounds such as alkenyl succinic acid or ester moietiesthereof, benzotriazole-based compounds and thiodiazole-based compoundsmay be conveniently used in the lubricating compositions as corrosioninhibitors.

Compounds which may be conveniently used in the lubricating compositionsof the present invention as seal fix or seal compatibility agentsinclude, for example, commercially available aromatic esters.

The lubricating compositions of the present invention may beconveniently prepared by admixing the volatility reducing additive, andany optional additives, with the base oil(s).

The above-mentioned additives are typically present in an amount in therange of from 0.01 to 35.0 wt. %, based on the total weight of thelubricating composition, preferably in an amount in the range of from0.05 to 25.0 wt. %, more preferably from 1.0 to 20.0 wt. %, based on thetotal weight of the lubricating composition.

Preferably, the lubricating composition contains from 10 wt. % to 15 wt.% of an additive package comprising a combination of additives includinganti-oxidants, a zinc-based anti-wear additive, an ashless dispersant,an overbased detergent mixture, and a silicone-based anti-foaming agent.

In another aspect, the present invention provides the use of avolatility reducing additive to lower NOACK volatility of a lubricatingcomposition, in particular wherein the lubricating composition comprisesa Fischer-Tropsch derived base oil.

Also the present invention provides a method of improving NOACKvolatility properties, which method comprises lubricating the crankcaseof an engine, in particular a passenger car motor engine, with alubricating composition according to the present invention.

The present invention is described below with reference to the followingExamples, which are not intended to limit the scope of the presentinvention in any way.

Examples

Lubricating Oil Compositions

Various engine oils for use in a crankcase engine were formulated. Table1 indicates the properties for the base oil used.

TABLE 1 Base oil 1 (GTL 4) Kinematic viscosity at 100° C.¹ [cSt] 4.1 VIIndex² 125 NOACK volatility³ [wt. %] 12.5 ¹According to ASTM D 445²According to ASTM D 2270 ³According to ASTM D 5800B

Table 2 indicates the composition and properties of the fully formulatedengine oil formulations that were tested; the amounts of the componentsare given in wt. %, based on the total weight of the fully formulatedformulations.

All tested formulations contained a combination of a base oil andadditive, wherein the base oil in each case was GTL 4.

“Base oil 1” was a Fischer-Tropsch derived base oil (“GTL 4”) having akinematic viscosity at 100° C. (ASTM D445) of approx. 4 cSt (mm²s⁻¹).This base oil may be conveniently manufactured by the process describedin e.g. WO-A-02/070631, the teaching of which is hereby incorporated byreference.

“Additive A” was a dispersant, Infineum C9280, which is commerciallyavailable from Infineum.

“Additive B” was an aminic antioxidant, Infineum C9452, which iscommercially available from Infineum.

“Additive C” was a molybdenum based friction modifier, Infineum C9455,which is commercially available from Infineum.

The compositions of Examples 1 to 3 and Comparative Example 1 and 2 wereobtained by mixing the base oils with the additive, where present, usingconventional lubricant blending procedures. The results of NOACKvolatility testing via ASTM D5800B are shown in Table 2.

TABLE 2 Component Comp. Comp. [wt. %] Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3Additive A 0 1.0 0 0 0 Additive B 0 0 0.5 1.5 0 Additive C 0 0 0 0 0.7GTL 4 100 99.0 99.5 98.5 99.3 Total 100 100 100 100 100 NOACK, %/m 12.512.6 11.8 11.6 11.0

DISCUSSION

As can be learned from Table 2, Examples 1-3, which contain a volatilityreducing additive, have significantly lower NOACK volatility values thanComparative Examples 1 and 2, which do not contain a volatility reducingadditive. These results are particularly surprising because eachadditive included in the formulations shown for Examples 1-3 iscomprised of a concentrate wherein the additive has been diluted in abase oil with NOACK volatility of greater than 12.5% as measured by ASTMD5800B, thus the expectation is that addition of the additives inExamples 1-3 will increase NOACK volatility rather than decrease it.

An important benefit of the present invention is that for future lowviscosity engine oils such as 0W-16 (as per SAE J300 table of engine oilviscosity grades) and lower viscosities (0W-12, 0W-8, etc), stringentNOACK volatility requirements can be met with lesser or no need to use(relatively expensive) poly-alpha olefin (PAO) base oils.

Given these findings, it is expected that many other chemistries mayimpart similar benefits in serving to lower NOACK volatility, such asknown lubricant additive chemistries (anti-wear, anti-oxidant, viscosityindex improver, friction modifier, detergent, dispersant, pour pointdepressant, etc) and any other chemical species that interacts stronglywith the oil-air interface so as to lower the rate of evaporationincluding but not limited to surfactants, functionalized polymers, ionicliquids, nanoparticles, etc.

1. A lubricating composition comprising: (i) a base oil; (ii) volatilityreducing additives; wherein the volatility reducing additives comprisesa molybdenum based friction modifier and an aminic antioxidant; andwherein the composition has a kinematic viscosity at 100° C. (accordingto ASTM D445) of 16.3 mm2/s or less, a low temperature crankingviscosity of at most 6200 cP at −35° C. (ASTM D5293) and a NOACKvolatility of at most 15% according to ASTM D5800B.
 2. The lubricatingcomposition according to claim 1, wherein the composition has a NOACKvolatility of at most 12.5% according to ASTM D5800B.
 3. The lubricatingcomposition according to claim 1, wherein the molybdenum based frictionmodifier is present in the range of from 0.5 wt. % to 5 wt. % withrespect to the total weight of the lubricating composition.
 4. Thelubricating composition according to claim 1, wherein the an aminicantioxidant is present in the range of from 0.5 wt. % to 5 wt. % withrespect to the total weight of the lubricating composition.
 5. Thelubricating composition according to claim 1, wherein the base oilcomprises one or more Fischer-Tropsch derived base oils.
 6. Thelubricating composition according to claim 5, wherein the base oilcomprises 80% or greater of one or more Fischer-Tropsch derived baseoils, by weight of the base oil.